An important goal of nanotechnology is bottom-up manufacturing of useful devices and materials via self-assembly at room temperature in environmentally benign solvents. Living systems provide numerous examples of such self-assembly in the guise, for example, of protein structures such as microtubules,1 viral capsids,2 bacterial s-layers,3 and amyloid fibrils4 in which proteins grow in one-dimensional filaments with β-strands perpendicular to the growth axis.
The programmable design of DNA-based nanostructured scaffolds is extraordinary,5 allowing for the templating of ordered heterogeneous arrays of, e.g., metallic nanoparticles,6 proteins,7 and semiconducting wires.8 However, it is plagued with technical barriers to advancement, including: a) difficulties in scaling it to industrial applications, b) high error rates of DNA replication, c) denaturation of DNA scaffolds/bundles at moderate temperatures (˜60° C.), and d) loss of integrity under exposure to ultraviolet light and enzymes,9 e) very limited capability to carry a broad range of functional groups; f) limited tenability in terms of ternary and quaternary structures.
Belcher and collaborators have used the M13 virus as a scaffold for self-assembly of a wide variety of inorganic materials. Their strategy relies on modifying coat proteins with peptides that are selected through phage display for templating a specific material.10 In one example, the M13 major coat protein was coated by a peptide with FePO4-nanoparticle templating activity while the attachment proteins at the end of the virus were fused to a peptide known to adhere to carbon nanotubes.11 Incubation of the virus with iron and phosphate ions together with single-walled carbon nanotubes generated a self-assembled working cathode. However, the M13 approach is limited by several factors: (a) viruses are large (M13 is nearly a micron in length); (b) templating sites are limited to the coat proteins, and the geometry is restricted to that provided by the virus; (c) while the viruses can order as liquid crystals, the ordering is on the micron scale; and (d) the capability to engineer or program designed structure is difficult as the product is at the mercy of viral scaffold. Hence, precise, programmable nanometer-scale ordered heterogeneity, as achieved with DNA, is not feasible.
Amyloid fibrils are self-assembled one-dimensional protein arrays with fi-strands perpendicular to the linear axis.4 They arise both in unregulated self-assembly in numerous diseases including Alzheimer's disease and type II diabetes, as well as in regulated contexts in biofilm extracellular matrices,12 synapse formation,13 and hormone reservoir manufacture.14 These fibrils have bending and twisting persistence lengths on the micron scale,15, 16 which contribute to the remarkable tensile strength of spider silk17 and the structural stability of barnacle cement.18 They have previously been used to template metallic nanowire growth,19-21 and have been used to produce mechanically strong oriented films.22 
Amyloid structures are remarkably robust. Generally, they can survive heating to the boiling point of water23-25 although there is monomer size and sequence dependence to this result. They are resistant to protease degradation26, 27 and UV light exposure. To date, amyloids have not been assembled to produce a significant level of transverse order, nor have they been used to template material growth other than the examples given above. There is also little systematic understanding of amyloid structure because the lack of transverse order makes it difficult for X-ray diffraction to reveal more than the generic cross β-stacking,28 although in some instances additional scattering rings in fiber diffraction have provided information about transverse dimensions of fibrils and longer periodicity repeats along the fiber axis.29 